In a basic service set (BSS), STAs may communicate with an access point (AP) over a common communication channel of a wireless medium. Only one STA is able to communicate with the AP at a time. To avoid collisions, STAs may use a technique called Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) to sense whether the wireless medium is idle before attempting to transmit to the AP. When more than one STA seeks to transmit to the AP at the same time, the STAs may go through a contention process for access to the wireless medium. Once a STA wins the contention and gains access to the wireless medium, it may transmit to the AP.
A STA may support a power-save mode in which the STA enters an awake state when it has an uplink packet to send (or downlink packet to receive) and then switches to a doze state when transmission of the packet is complete. In the awake state, the STA may be fully powered. In the doze state, the STA may consume very low power and may not be able to transmit or receive.